This article was originally published on the defunct Ancient World Magazine website and is now re-published here.
The Pantheon in Rome is one of the best-known structures in the city, visited by countless tourists in years when we aren’t all suffering from the strains of a global pandemic. It is also one of the best-preserved ancient monuments in Rome, as it was turned into a Christian church in the early seventh century AD, ensuring it would remain more or less intact for many years to come.
The name by which it is known, “Pantheon”, derives from the ancient Greek meaning “of all the gods”. Most ancient temples were dedicated to one deity, like the Parthenon in Athens (dedicated to Athena), or a small group of deities, like the Temple of Mars Ultor in Rome. The latter was dedicated by Augustus and featured the statue of Mars Ultor (“Mars the Avenger”), flanked by a statue of Venus (his lover; also the ancestral deity of the Julii) and the deified Julius Caesar (whom Augustus had avenged).
But this building is probably even more noteworthy for its construction. The inside of the drum is impressive: the dimensions are such that a giant sphere 145 Roman feet in diameter (or a little over 141 modern feet, i.e. 43m) would fit snugly inside, with the top curving along with the inside of the domed ceiling. While much of the interior marble still visible today was added later, it almost certainly gives an impression of what the structure originally looked like on the inside. The biggest difference between the Pantheon as it is today and what it looked like back in ancient times is that originally the ceiling was gilded. At the front of the building is a monumental porch with sixteen granite columns. Another rectangular structure is found at the back, with rooms and stairs.
Like many monumental buildings in ancient Rome, the Pantheon was made from brick, concrete, marble, and other types of stones. The concrete was mixed with other materials (aggregate). Close to the ground, heavy materials were mixed with the concrete, such as heavy travertine. As one moves up along the structure, the builders used progressively lighter materials, such as a mixture of travertine and tufa, and at the very top they mixed the concrete with the lightest type of rock they could find: pumice, which is so light that it – at least initially! – floats when thrown in water.
To make the ceiling even lighter, the builders used a technique known as coffering: coffers are the rectangular indentations that you notice when looking up at the ceiling, used for decorative effect as well as a way of making the dome itself thinner and lighter. You can find these coffers in other buildings of the Classical period (ca. 500 BC to AD 500) as well, such as the Temple of Hephaestus in Athens, another well-preserved ancient structure.
The date of its construction
It is generally thought that the Pantheon was constructed during the reign of the emperor Hadrian (r. AD 117-138). However, the inscription at the front of the building reads as follows:
Most Roman inscriptions are fairly formulaic and so you don’t need to know a lot of Latin in order to figure this one out. “M. Agrippa” is a name (Marcus Agrippa). “L.F.” stands for Lucii filius (i.e. son of Lucius): the total number of Latin names is rather limited, so it was necessary to provide as many specifics as possible to indicate which “M. Agrippa”, in this case, was meant. Cos. tertium here dates the inscription: it refers to Agrippa’s third term as consul. Finally, fecit is the past perfect tense of facere (“to make”); the full inscription can thus be translated as “Marcus Agrippa, the son of Lucius, made [this] when he was consul for the third time”.
The Agrippa referred to in this inscription must have been Marcus Vipsanius Agrippa. He had been the son-in-law and one of the closest friends of Augustus (r. 27 BC to AD 14), the first Roman emperor. But why was this man, who had lived a century earlier, credited with building the Pantheon? The reason was that the Pantheon occupied the site of two earlier buildings that had both been dedicated by him, including an earlier Pantheon. Hadrian was simply too humble, so the story goes, to attach his own name to the building and so had the Pantheon credit Agrippa as the builder.
But was the Pantheon really built during in the time of Hadrian? This is the subject of a relatively recent – as far as academic publications are concerned – chapter in the book The Pantheon: From Antiquity to the Present (2015, pp. 79-98), edited by Tod A. Marder and Mark Wilson Jones. The chapter is entitled “New perspectives on the dating of the Pantheon” and was written by Lise M. Hetland.
Hetland points out that the written sources that claim that the Pantheon was erected in Hadrian’s time are contradictory. The idea that Hadrian was supposedly too modest to inscribe his own name into the Pantheon’s facade originates from the Historia Augusta, a collection of biographies of Roman emperors that is not exactly known for its historical accuracy.
But what about the archaeological evidence? Many of the bricks used in the construction of the Pantheon feature stamps that allow them to be dated. These brickstamps point in a very specific direction: a large number of them date to the reign of Hadrian’s immediate predecessor, the emperor Trajan (r. AD 98-117).
It seems therefore likely that construction of the Pantheon began before Hadrian became the ruler of the Roman Empire. Hetland suggests that construction started in AD 114-116. It is even possible that builders started planning the construction of the new Pantheon shortly after a lightning strike in AD 110 caused part of this area of Rome to burn down (Orosius 7.12.5; Hieronymus ab Abr. 2126).
Whenever the Pantheon was constructed, it remains one of the key attractions to any visitor to Rome. Until the early 1990s, it was possible to climb the ancient stairs inside the walls to reach the roof, so you could peer down from the oculus and see the people below. That is, as far as I know, no longer allowed today. A pity, but it doesn’t make the Pantheon any less worth your attention.
This article has been reworked from two earlier texts by the present author that were published elsewhere on the internet. One of these older articles benefited from the comments of archaeologists Edwin de Vries, who did research into the bricks used in building the Pantheon.